Examples:

• One would simply be at a loss for words.
• I'm usually not at a loss for words.
• First time I've seen your dad at a loss for words.
• The motivational speaker's finally at a loss for words.
• Are you at a loss for words when starting that important letter?
• But I got to tell ya, I'm at a loss for words.
• I've never seen you at a loss for words, young man:
• Here we are, and I'm at a loss for words.
• For the first time ever, I'm at a loss for words.
• I'm at a loss for words, 'cause it was so unexpected.